1. Field of the Invention
This invention relates to a plasma display device, and more particularly to a plasma display panel that is adapted to make use of a radio frequency discharge.
2. Description of the Related Art
Recently, a plasma display panel (PDP) feasible to the fabrication of large-scale panel has been available for a flat panel display device. The PDP controls a discharge interval of each pixel to display a picture. Such a PDP typically includes a PDP of alternating current (AC) system having three electrodes and driven with an AC voltage as shown in FIG. 1.
FIG. 1 shows the conventional AC system PDP having discharge cells arranged in a matrix pattern. The discharge cell includes a sustaining electrode pair 12A and 12B formed on an upper substrate 10 sequentially, an upper plate having an upper dielectric layer 14 and a protective film 16, and a lower plate having an address electrode 20, a lower dielectric layer 22, a barrier rib 24 and a fluorescent layer 26. The upper substrate 10 and the lower substrate 18 are spaced, in parallel, by the barrier rib 24. The sustaining electrode pair 12A and 12B consists of a scanning/sustaining electrode and a sustaining electrode. A scanning signal for a panel scanning and a sustaining signal for a discharge sustaining are applied to the scanning/sustaining electrode 12A while a sustaining signal is applied to the sustaining electrode 12B. An electric charge is accumulated into the upper dielectric layer 14 and the lower dielectric layer 22. The protective film 16 prevents a damage of the upper dielectric layer 14 due to the sputtering, thereby prolonging a life of PDP as well as improving an emissive efficiency of secondary electrons. Usually, MgO is used as the protective film 16. The address electrode 20 is crossed with the sustaining electrode pair 12A and 12B. A data signal is applied to the address electrode 20. The barrier rib 24 is formed in parallel to the address electrode 20. The barrier 24 prevents an ultraviolet ray produced by a discharge from being leaked into the adjacent cell. The fluorescent layer 26 is coated on the surface of the lower dielectric layer 22 and the barrier rib 24 to generate any one of a red, green, and blue visible lights. An inactive gas for a gas discharge is injected into an inner discharge space.
The PDP cell having the structure as described above sustains a discharge by a surface discharge between the sustaining electrode pair 12A and 12B after being selected by an opposite discharge between the address electrode 20 and the scanning/sustaining electrode 12A. In the discharge cell, the fluorescent body 26 is radiated by an ultraviolet ray generated during the sustaining discharge to emit a visible light into the exterior of the discharge cell.
Such a PDP controls a discharge-sustaining interval, that is, a sustaining discharge frequency of the discharge cell to implement a gray scale required for an image display. Accordingly, the sustaining discharge frequency becomes an important factor for determining the brightness and a discharge efficiency of the PDP. For the purpose of performing such a sustaining discharge, a sustaining pulse having a duty ratio of 1, a frequency of 200 to 300 kHz and a width of about 10 to 20 .mu.s is alternately applied to the sustaining electrode pair 12A and 12B. The sustaining discharge is generated only once at an extremely short instant per the sustaining pulse by responding to the sustaining pulse. Charged particles generated by the sustaining discharge are moved along a discharge path formed between the sustaining electrode pair 12A and 12B in accordance with the polarity of the sustaining electrode pair 12A and 12B and accumulated in the upper dielectric layer to be left into a wall charge. This wall charge lowers a driving voltage during the next sustaining discharge, but reduces an electric field in the discharge space during the corresponding sustaining discharge. Accordingly, when a wall charge is formed during the sustaining discharge, a discharge is interrupted. As described above, the sustaining discharge is generated only once at an extremely shorter instant than a width of the sustaining pulse, and it is consumed for a formation step of wall charge and a preparation step of the next sustaining discharge. Due to this, in the conventional PDP, a real discharge interval becomes very short in comparison to the entire discharge interval to have a low brightness and discharge efficiency.
In order to solve such a problem of low brightness and discharge efficiency, we has suggested a method of utilizing a radio frequency discharge using a radio frequency signal of tens of to hundreds of MHz. In the case of the radio frequency discharge, electrons perform an oscillating motion by the radio frequency signal to sustain the display discharge during a time interval when the radio frequency signal is applied. More specifically, when a radio frequency voltage signal having an alternately inverted polarity is applied to any one of the two opposed electrodes, electrons within the discharge space are moved toward one electrode or the other electrode depending on the polarity of the voltage signal. In the case where electrons are moved into any one electrode, if the polarity of a radio frequency voltage signal having been applied to the electrode before the electrons arrive at the electrode is changed, then a movement speed of the electrons is decelerated gradually and hence a movement direction thereof is changed toward the other opposed electrode. The polarity of the radio frequency voltage signal is changed before the electrons within the discharge space arrive at the electrode in this manner, so that the electrons do an oscillating motion between the two electrodes. Accordingly, when the radio frequency voltage signal is being applied, ionization, an excitation and a transition of gas particles are continuously generated without an extinction of electrons. The display discharge is sustained during most discharge time to thereby improve the brightness and a discharge efficiency of the PDP. Such a radio frequency discharge has the same physical characteristic as a positive column in a glow discharge structure.
The conventional PDP having the cell structure shown in FIG. 1 is unsuitable for making use of the above-mentioned radio frequency discharge. In other words, in order to utilize the radio frequency discharge as the display discharge, a distance between the two electrodes must be assured sufficiently. However, in the AC system PDP of FIG. 1, since the scanning/sustaining electrode 12A and the sustaining electrode 12B are spaced in a very short distance on the same plane, a radio frequency discharge is not caused as long as a frequency of the radio frequency signal is very high. Accordingly, it is necessary to provide a PDP having a structure suitable for making use of the radio frequency discharge.